Transfer of solids



May 12, 1959 w. E. COOPER ET AL 2,886,210

TRANSFER oF soLIns Filed sept. 28, 1956 A TTOR/VEKS United States Patent2,886,210 TRANSFER or soLrDs Wayne E. 'Cooper and Walterl C. Pouppirt,Bartlesville,

Okla., assignors to Phillips Petroleum Company, a corporation ofDelaware t This invention relates to amethod for transferringsubdividedsolids. In one aspectit relates to a process in which solidsare settled from a slurry as a compact mass and transferred while inthis form by the application of fluid pressure. Y In another aspect theinvention relates to the transfer of wet-compacted solids by the use ofa displacing fluid, the quantity of solids transferred being controlledby controlling the quantity of said luid.y

The simultaneous movement and measurement of solids presents a difficultproblem in that conventional oW measuring devices are unable towithstand the erosive effect of solids for any appreciable period oftime. One device frequently used is a positive displacement pump butthis type of apparatus providesl accurate measurement for only a limitedtime', after which either replacement or repair of the pump becomesnecessary.

It is an object of this invention to provide an improved process fortransferring solids.

Another object of-this invention is to provide an improved process fortransferring wet finely divided compacted solids.

Still another object of this4 invention is to provide an improvedprocess for transferring wet and nely divided K solids in a compact massand measuring the quantity of said solids transferred.

' Yet another object ofA this invention is to provide an improvedprocess for transferring wet nely divided solids,

comprising chromium oxide containing hexavalentl chromium onsilica-alumina, in a compact mass and measuring the quantity of saidsolids transferred.

Thesey and other objects of the invention will become more readilyapparent from the following detailed description :and discussion.

The transfer of solids in the method of' this invention is achievedbroadly vby displacing a wet' compacted solids mass from a conined zonewith a fluid and measuring the quantity of displacing tluid to determinethe quantity of solids transferred'. In one aspect of the invention thetransferred`y solids arelcompacted by` settling the solids from asolids'` slurry. In another aspect of the invention the solids andliquid are introduced separately to the confined zone whereby wettingand compaction-fof the solids is provided. In` still' another aspect ofthe' invention the transferred solidsA are wetted and compacted byintroducing dry solids to a liquid accumulatedA in the conned zone.

This invention isapplicable to the treatment of `solids in general, suchas for' example, inert materials like sand, carborundum, pumice, etc.,materials suitable for conversion to reaction products, like coal,shale,\lignite, etc., and catalytic materials llike metals, metaloxides, for example, silica, alumina silica-alumina, etc. The solids aresubdivided to provide materials whch are readily compacted when'wet. v

Although any of the solids listed are suitable for treatment in themethod of this invention, the invention is particularly applicable inthe handling ofvcatalytic materials and in its preferred embodiment'isdirected to the compacting and transferring of catalysts which areemployed 2,886,210 :.'Ftente'l-M'ayf k112,- 119592 in theYpolymerization o f ole'n'ic'` materials tov solid polym'ers'thereofi`"The olefin polymerization process can be used to produce a widevariety-ofolen polymers, such yas, for example: polymers or 'copolymers'of mono-olens like ethylene, propylene, butylene, etc.; also copolymersof mono-olens and dioleflns such as butadiene, isoprene, etc. Thesepolymers are prepared usually by contacting the olefin to bepolymerizedlwith a catalyst in the presence ofv a solvent kor diluentmaterial at an elevated temperature and pressure. `A number of catalyticmaterials can be used for the purpose of polymerizing olens, the mostdesirable being chromium oxide, preferably containing hexavalentchromium, associated with silica, alumina, zirconia, thoria,silica-alumina, etc. These catalysts can be prepared, for example, bycontacting soluble salts of chromium with silica, alumina, thoria,etc.,y for a suiilcient .Y to the' copending application of Hogan andBanks, Serial No. 573,877, filed March 26, 1956, now Patent Number2,825,721, issued March 4, 1958, wherein the catalysts are discussed in.detail. These and' other solid catalysts or catalysts containing a solidcomponent can be treated in the method of this invention.

The temperature required for polymerizing olefns varies over a widerange. However, usually it is preferred to carry out the reaction at atemperature between about 150 F. and about 450 F. The particulartemperature to be employed in each individual case depends on thecatalyst used, the` olen to be polymerized and the operatingconditionsemployed, such as pressure, space ve-l locity, diluent to olenratio, etc.

The polymerizationpressure is maintained at a suflcient level to assurea liquid phase reaction, that is at least about to 300 p.s.i.g.,vdepending upon the type of feed material, diluent and the polymerizationtemperature. Higher pressures upto 500 to 700 p.s.i.g. or higher can beused, if desired. The catalyst concentration in the reaction zone ismaintained between about 0.01 and about l0 percent by weight. Genera11y,it is desirable to provide a reactant residence time of between about 15minutes and about 12 hours.

The useV of adiluent in the polymerization reaction in general servest'wo'purposes. Since the reactions are usually exothermic in nature, thepresence of a quantity of diluent provides a method for obtaining closecontrol of the reactiontemperature. In addition, polymers formed in thereaction, or a portion thereof may be tacky in nature yand,if thisisthe' case,`the presence of a diluent tends to` preventadherence of thepolymer to the walls of the reaction vessel and the` recovery equipmentwhich is used in treating the eluent from the'polymerizationreaction. Ingeneral, thequantity of diluent is large relative to the olen feedmaterial. Usually, the olen` constitutes between about 0;'1l and about25 percent by volume of the mixture and preferably between about 2 andabout 15 percent by volume. p

The solvent or diluent employed in the polymerization reaction includesin general, parain hydrocarbons. Among themore `useful solvents areacyclic parains having between aboutv 3 and about l2 carbon atoms permolecule, lsuch as, ,for example, propane, isobutane, npentane,isopentane, isooctane, etc. and preferably those acyclic paraffinshaving 5 to 12 carbon atoms per molecule. Also useful in thepolymerization reaction are alicyclic hydrocarbons, such as cyclohexane,methylcyclohexane, etc. Aromatic diluents are also used, however, insome instances they (or impurities therein) tend to shorten the catalystlife, therefore, their use will depend on' the'` importance of catalystlife.. Allof lthe foregoing and in addition, other hydrocarbondiluentsfwhich are relatively inert and in the liquid state at thereaction conditions may also be employed in carrying out the reactiono`olens to form solid polymers..

l In carrying out the invention in one embodimentY thereof nely dividedsolids such as chromium oxide catalyst containing hexavalent chromiumsupported on silicaaluminum are introduced as a slurry in a liquid to asettling zoneLwherein the solids separate from the liquid and ,formL wetcompact mass. When a predetermined level of solids is obtained in'thesettling zone theiow of slurry is terminated and the compact solidsmassis forced from the lower portion of the settling zone by-the applicationof fluidpressure to the top of the solids mass. With a knowledge of thesolids content of the compacted mass, such as by periodical sampling andanalysis, the ow rate of the transferred solids can be measured byappropriately controlling the rate of introduction of the pressuringfluid to thel settling zone. `Controlof the fluid flow rate can beobtained by `the use of conventional instrumentation for measuring uidow and/ or by providing a suitable means for transferring the uid suchas a positive displacement pump, which controls the rate of flowingfluid.

It is desirable when introducing the slurry of solids and liquid to thesettling zone to provide a minimum of turbulence whereby the solids aresettled from the liquid in a short period of time. Thus, it has beenfound preferable to introduce the slurry to the settling zonetangentially whereby a minimum of disturbance of the liquid and solidscontained therein occurs.l

The transfer'of solids in the method of this invention is based on thefacty that when solids of an appropriate size distribution are settledin a liquid the wetted solids form a compact mass which can be movedthrough a confined zone by a pressuring uid without appreciablepenetration of the fluid into the solid mass. Thus, it is possible totransfer solids from such a mass, without substantially changing therelative proportions of solid and liquid, whereby the quantity of thepressuring iluid provides a direct measurement of the quantity of solidsbeing transferred. With respect to solids size, it has been found'thatin general, successful operation of the invention is promoted by solidsof small particle size. Thus, there is substantially no limit to theminimum particle size which can be employed. However, as the particlesize becomes greater the void space can increase to the point where thepressuring uid will begin to penetrate the solids mass and when asufiiciently large solids particle size is reached, the propelling fluidwill pass completely through the compacted solids. It has been foundthat ifa solid of a single particle size is employedthat the maximumparticle size which can be used to successfully provide a wet solid masswhich is substantially impenetrable to the pressuring `fluid is betweenabout 4() and about 60 mesh. When, as in ordinary commercial operations,the solids mass covers a range ofparticle size it is possible to employin conjunction with the size range given both smaller particles andparticles of a larger'size up to and including about one-quarter of aninch. In general, however, the average particle size should be notgreater than between about 40 and about l mesh. I

The composition of the wet compacted solids mass being transferred willvary depending upon the particular solids and the particular wettingliquid employed. In general, the solids on a volume basis comprisebetween about r25 and about 90 percent of the total mass. For example,.when transferring a chromium oxide catalyst containing hexavalentchromium supported on silica aluminum wetted with cyclohexane thecompacted solids comprlse approxlmately 52 percent by volume of thetotal mass and the total mass has a density of about 60 pounds per cubicfoot.

It is within the scope of the invention to provide transfer of the wetcompacted solids from the settling zone by the use of either a gaseousor a liquid pressuring uid. inasmuch as liquids are substantiallyincompressible the problem of measuring liquid ow introduces fewerproblems than the measurement of gas ow. Therefore, a liquid fluid isusually preferred. However, in some instances it may be desirable to usea gas for the pressuring fluid rather than a liquid. F or example, inthe polymerization of ethylene with a chromium oxide catalyst containinghexavalent chromium associated with silica-alumina, it is possible touse ethylene gas as a pressuring medium. Since this gas is employed as areactant in the polymerization reaction there is no problem ofcontamination when operating in this manner. y

When utilizing a liquid pressuring fluid it is usually preferable thatthe slurrying liquid and the pressuring liquid be the same. Whencarrying out the polymerization of ethylene as previously `described thepressuring liquid can be selected from any of the solvents listed in thediscussion of the polymerization process. The slurrying and pressuringliquid in any particular instance will be determined by the particularsolids vto be transferred and the service in which the solids are to beemployed. Any liquid whichpis capable of wetting solids for compactioncan be used within the scope of the invention.

In the embodimentof the invention just discussed the solids areintroduced to the settling zone in the form of a slurry. While this isthe preferred method of operation it is within the scope of theinvention to introduce the solids to the settling zone for the-formation of the wet compacted mass inother manners. For example, drysolids can be introduced to the settling zone into a wetting liquidaccumulated therein. When operating in this manner, it may be desirableto provide agitation of the liquid during the lling cycle in order toassure uniform wetting of the solids. It is also within the scope of theinvention to separately and simultaneously introduce the wetting liquidand solids to the settling zone. Here again it may be desirable tofurnish agitation in order to assure uniform wetting and compaction ofthe solids.

In order to more clearly dene the invention and provide a betterunderstanding thereof reference is had to the attached drawing which isa diagrammatic illustration of a catalyst solids settler and a reactorfor the polymerization of olens. Referring to the drawing catalystsolids subdivided'to provide a range of size between about 20 and 60mesh, comprising chromium oxide containing hexavalent chromiumassociated with silica alumina, slurried in cyclohexane are introducedthrough conduit 5 to settler 2. In order to facilitate separation andcompaction of the solids the slurry is introduced to the settlertangentially. The flow of slurry to the settler is continued until thesettler is substantially full of compacted solids. To provide thisquantity of solids'requires a total feed which is` substantiallykgreater thanthe settler volume. Accordingly, provision is made to removeexcess slurrying liquid from the top ofthe settler through conduit 6.When the solids in the settler reach the desired predeterminedlevel th'eow of the slurry is terminated and a pressure is applied to the top ofthe settler by introducing cyclohexane through positive displacementpump 8 and conduit 7. When the pressure in the settler reaches asufficient level above the pressure in the reactor, the valve in conduit9 is opened and compacted solids are pressured from the bottom of thesettler throughconduit 9 into reactor 3. At the same time additionalcyclohexane and volefin are introduced to the reactor through conduits11 and 12 respectively. Within the reactor suitable conditions oftemperature and pressure are maintained, namely about 285 F. and about500 p.s.i.a whereby ethylene is converted to assetato solid polymers. Toaid in the reaction eciency and maintain a catalyst in suspensionagitation of the contents of the reactor is provided by a motor drivenmixer 10. Eluent from the reactor, comprising polymer, cyclohexane,catalyst and unreacted ethylene is passed to a separation zone 4 whereinseparation and recovery of ethylene, catalyst, cyclohexane and polymertakes place, these materials being yielded through conduits 14, 15, 16and 17 respectively.

The compaction of settled catalyst within settler 2 is such that thedisplacing liquid which enters the settler through conduit 7 penetratesthe catalyst mass only a very short distance. Thus, it is possible todisplace solids of a substantially constant composition from the settleruntil this vessel is almost entirely empty. Since the composition of thesolids mass does not vary appreciably measurement of the propelling ordisplacing liquid provides a measurement of the quantity of solidsintroduced to the reactor. Control of the displacing liquid rate can beprovided by suitable instrumentation or as in the present specificexample by introducing the displacing liquid to the settler through apositive displacement pump.

When the solids settler is substantially emptied the ow of displacingliquid is terminated and the solid slurry is again introduced to thesettler repeating the operation previously described until the settleris again substantially filled with compacted solids. In order tomaintain a continuous flow of catalyst to the reactor it is necessarythat several settlers be provided to operate in parallel.

The following example is given in illustration of a typical applicationof a preferred embodiment of the invention on a commercial scale.

Example Subdivided chromium oxide catalyst (40 to 60 mesh) containinghexavalent chromium associated with silica alumina is slurried incyclohexane and introduced tangentially to a rst settler at a rate ofabout 1800 lbs. per hour, of which about 180 lbs./hr. comprises solidsand the remainder cyclohexane. The settler vessel comprises an elongatedcylindrical tank having a conical bottom and a volume of about 55 cubicfeet. Within the settler the solids and liquid separate, wetted solidsaccumulating in the bottom of the settler in a Wet compacted masscontaining about 51 percent of solids by volume and'having a mass ofabout 60 pounds per cubic foot. Flow of catalyst slurry to the settleris continued for a sufficient period of time to substantially ll thesettler with compacted solids, excess liquid being withdrawn overheadfrom the top of the settler. At this point the flow of slurry isdiscontinued and cyclohexane is introduced to the top of the settlerthrough a positive displacement pump at a rate of about 0.37 gal. perminute. The bottom of the settler is then opened through conduit 9,which is a standard 2 inch pipe, to reactor 3 which is operated at atemperature of about 285 degrees F. and a pressure of about 500 p.s.i.a.to carry out the polymerization reaction. When the pressure in thesettler reaches a sufcient level to overcome the friction drop throughconduit 9, namely about 515 p.s.i.a., compacted catalyst is pressuredfrom the settler through this conduit and enters the reactor at a rateequal to the flow of pressuring liquid to the settler. Based on thecomposition of the compacted solids previously given the catalyst feedrate is thus controlled to provide about 91 pounds of fresh catalystentering the reactor per hour. Simultaneous with the passage of catalystinto the reactor ethylene is introduced thereto at a rate of about11,500 pounds per hour and additional cyclohexane is added to provide adiluent-to-polymer ratio in the reactor of about 11.73 to 1. Within thereactor the polymerization reaction provides a solid ethylene polymerproduct, during which process about 60 percent of the olefin feed isconsumed. The reactor efuent, comprising polymer product, unreactedethylene, cyclohexane and catalyst is passed through a series ofseparation steps 6 wherein the various components are separated and asuitable polymer product is obtained.

Pressuring of catalyst from the rst settler is continued until aboutpercent of this material has been removed. At this time the flow ofdisplacing liquid is terminated. During the time when the irst settleris being emptied a second settler is being illed with compacted solidsin the previously described manner. When the flow of displacing liquidto the rst settler is terminated this liquid is transferred to thesecond settler and compacted catalyst from the latter settler is thenintroduced into the reactor. In order to prepare the first settler foruse when the second settler becomes emptied, slurried catalyst is againintroduced to the rst settler and lling of this settler is carried outin the manner previously described. When operating in the foregoingmanner, it is possible to provide a metered, constant quantity ofcatalyst to the reactor without passage of solids through any type ofmetering or control instrument.

Having thus described the invention by providing a specific examplethereof, it is to be understood that no undue limitations orrestrictions are to be drawn by reason thereof and that manymodifications and variations are within the scope of the invention.

We claim:

1. A process for transferring subdivided solids which comprises feedingsolids and liquid to a confined zone wherein the solids settleV from theliquid to form a wet compacted mass, introducing an additional quantityof said liquid under pressure to the confined zone, pressuring compactedsolids from the confined zone with the additional liquid and controllingthe rate of ow of said solids by the rate of introduction of theadditional liquid.

2. The process of claim 1 n which the solids and liquid are introducedseparately to the confined zone.

3. The process of claim 1 in which the liquid is first introduced to theconfined zone and the solids are then introduced to liquid accumulatedin said zone.

4. The process of claim 1 in which the solids and liquid are introducedto the confined zone as a slurry.

5. The process of claim 4 in which the solids slurry is introducedtangentially to the confined zone.

6. A cyclic process for transferring subdivided solids comprisingchromium oxide containing hexavalent chromium associated withsilica-alumina which comprises feeding said solids and cyclohexane to aconned zone wherein the solids settle from the liquid to form a wetcompacted mass, discontinuing the feed to the confined zone when apredetermined level of compacted solids is obtained, introducingadditional cyclohexane under pressure to the confined zone, pressuringcompacted solids from the confined zone with the additional cyclohexane,and controlling the rate of ow of said solids by the rate ofintroduction of the additional cyclohexane.

7. The process of claim 6 in which the solids and liquid are introducedseparately to the confined zone.

8. The process of claim 6 in which the liquid is rst introduced to theconfined zone and the solids are then introduced to liquid accumulatedin said zone.

9. The process of claim 6 in which the solids and liquid are introducedto the conined zone as a slurry.

10. The process of claim 9 in which the solids slurry is introducedtangentially to the confined zone.

References Cited in the le of this patent UNITED STATES PATENTS1,553,476 Schuster Sept. 15, 1925 2,638,424 Hansgirg May 12, 19532,680,084 Ryan June 1, 1954 2,713,037 Kimberlin July 12, 1955 2,721,226Ciapetta et al. Oct. 18, 1955 FOREIGN PATENTS 268,667 Great Britain Apr.7, 1927 431,755 France Nov. 20, 1911

